Removing the heat electronic devices generate during operation has always been a concern. Addressing thermal management requires an understanding of the physics of heat generation and transfer (i.e., conduction, convection and radiation). Thermal management of devices operating well above absolute zero (e.g., 150° K and above) has long been understood. As a result, effective active and passive cooling techniques exist for such devices.
However, many near-future applications for devices, such as quantum computers, will require devices that operate very close to (e.g., within a few degrees Kelvin and perhaps small fractions of a degree of) absolute zero. Unfortunately, thermal management at such very low temperatures has proven quite complex and difficult. At very low temperatures, electrons become decoupled from the environment (a lattice of phonons) in which they travel as they flow through a material.
Two conventional thermal management techniques for very low temperatures exist. The first technique involves cooling the electrons before they go into the device. This is typically done by causing the electrons to pass through a large amount of very cold, porous metal. The large surface area of the metal keeps it cool. Unfortunately, this technique is problematic in that once the electrons enter the device, heat thereafter generated cannot be removed from them. U.S. Patent Application Publication No. 2007/0006583, filed by Veneruso on Jan. 11, 2007, entitled “Nanotube Electron Emission Thermal Energy Transfer Devices,” describes a related technique in which cold nanotubes are used to cool the electrons before they enter the device.
The second technique involves cooling the lattice of phonons as much as possible, with the hope that the electrons will couple enough to get cool. Unfortunately, electrons begin to decouple significantly from phonons at around 50 mK, at which point lattice cooling begins to be ineffective. Lattice cooling utterly fails below 10 mK.